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Technics SP-10 mkII speed adjustment question

Hi,

I'm on my way to complete my Technics SP-10 mkII project. Actually, a friend of mine, a professionnal audio technician, is working to upgrade the PSU, which is done but a small adjustment on the speed must be done and he need some cue on this issue.

We already asked Bill Thalmann, Artisan Fidelity and Oswald Mill audio. Plus, I'll post on DIY Audio today. We'd like to get the answer as quickly as possible to finalized this for the week-end. Hope someone on Audiogon can help.

Here's the message from my technician:

"Hello,

I'm an electronic technician and I do repair for audio equipments, vintage, hifi pro and more. I have a client here that brought me his turntable Technics Sp-10 MKII to fixed. I have a little question about it and he gave me your email because he pretended that you have some experience with this kind of materiel. So, hope that you can response my technical question.

I replaced all capacitors in the power supply and a big solder job. I checked for defect solders or capacitors on the circuit boards inside the turntable and I tied to do the adjustments . Everything seem good right now, the turntable work fine. I tried do do the period adjustment with the VR101 and VR102 potentiometers like in the service manual ( see attachment, Period adjustment method). When I looked the stroboscope at the front of the turntable, It's pretty stable but I can see a tiny rumble at 33 1/2 and 78 speed. 45 is the more stable speed for the stroboscope. So, I fixed the phase reference with T1 at 18us of period and I try to do the period adjustment at the point test T and S on the board with the O point for reference. When I put my scope probe on the T point, I can observe the stroboscope running. It is not stable at all. If I pull off my probe, the stroboscope is stable again. So When I have the 2 probes at point S an T at the same time to do the adjustment, it's impossible to fixed the wave T because it going right to the left on my scope. When I turned the VR101, the T wave going faster or slower but never stable. I tried to ground lift my scope, plug it into the same power bar and try to pull off the reference at the O point. I can't have a setup that I can see a stable T wave in my scope with the one that I can do the right adjustment. Why? Is there a problem with the turntable or maybe it's a incorrect probe or ground setup? Please let me know what you think.

Best regards"

Thanks for help,

Sébastien
128x128sebastienl

Showing 4 responses by lbelchev

lbelchev
64 posts
 
The sorry "glass" plinth by Technics was a joke and none of the tables you list has a plinth with even a fraction the effort and material that was put into ours.

Albert, Why do you think the Technics engineers were able to make the best turntable, but they were not able to design a suitable plinth?
lbelchev
64 posts
 
For the same reason Technics did not know to do the Krebs mods which raise speed stability and improve transparency and dynamics.

Albert, When Technics made their "mods" from Sp-10MK2 to Sp-10MK3 we see a clear improvement. This improvement reflected in the measurements of the Starting torque, Speed fluctuation, Wow and flutter, Rumble. Can we see some measurements before and after the Krebs mods?

There are precious few products manufactured 25 years ago that cannot in some way be improved through modern materials and technology that simply was not available back then.

The previous question applies to the modern materials too. Can we compare them with detailed measurements of the old anti-resonance materials - Kenwood Anti-Resonance Compression Base (ARCB), Sony Bulk Molding Compound (SBMC),Technics non-resonance compound (TNRC)?

The SP10 mk3 also has TNRC loaded in its chassis (you know the TNRC is not a "glass" ;-) Just this way (loading TNRC in the lower base), Technics have managed to bring down the Rumble from -86dB (MK2A) to -92dB (MK3).
lbelchev
64 posts
 
I would guess that the Mk2 and Mk3 are just so completely different that it was just fortuitous fall-out that resulted in the Mk3 having lower rumble.

Lewm, Out of question the Mk2 and Mk3 are completely different. Some of the differences are due to the different materials - respectively different technical data. This is from Technics SP-10MK3 brochure: "Also contributing to lower noise is the sophisticated cabinet construction featuring diecast zinc, diecast aluminum, and Technics original acoustic damping material TNRC (Technics Non- Resonant Compound) in the lower base. - 92 dB rumble means real silence; it's a difference you can hear from the moment you lower a stylus into the grooves." :-)

Moreover, somewhere around that time, the method for measuring TT rumble was changed such that the newer numbers were all about 3 db better than before.

Yes, This is the reason that I indicate the SP-10 mk2A rumble -86dB (IEC 98A) and the SP-10 mk3 rumble -92dB (IEC 98A). The SP-10 mk2 have different method for measuring -73dB (DIN 45539B).
lbelchev
64 posts
 
Lewm, When Technics wrote "sophisticated cabinet construction" they were referring to the chassis proper of the Mk3 only. Look at Halcro provided link from a cross-sectional view of the SP10Mk3 (it's from the same Technics MK3 brochure).
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